(1) Field of the Invention
The invention relates generally to the field of surface layers for objects, and more particularly to surface layers for reducing turbulence and drag in connection with an object moving through a fluid medium.
(2) Description of the Prior Art
In connection with the movement of objects, including, for example, torpedoes, towed sonar arrays, and submarines, and ships of many varieties, through a fluid medium such as the ocean, the reduction of turbulence, and accompanying drag, is very important. Increased turbulence and drag result in higher energy dissipation in connection with the movement, requiring a concomitant increase in the amount of energy applied to the object to accomplish movement. In addition, turbulence, in particular, caused by movement of an object in a fluid medium results in creation of noise. Larger amounts of turbulence, can increase the likelihood of the object being detected, which can be undesirable in warfare situations.
Over a number of years, efforts have been made to control and reduce turbulence created by movement of objects in fluid media. In one technique that has been developed, riblets have been formed on the surface of the object. This technique reduces drag somewhat, but it does little to help with turbulence. In addition, the drag reduction is only seen within a relatively narrow range of object speeds, which depend on the riblet geometry, and actually increase drag outside of the range. In a second technique, eddy break-up devices have been formed on the surface of the object. This can result in reduced drag in some cases, and also in a slight reduction in the noise due to turbulence, but the required devices generally comprise fairly large protrusions from the object. In a third technique, a fluid is actually injected from the object into the medium proximate the object's surface in regions susceptible to turbulence. This pushes the portions of the medium which might otherwise come into contact with the object generally away from the object, and also cushions the impact thereof onto the object, resulting in a reduction in the amount of turbulence and noise. This is achieved, however, with increase in cost due to the required plumbing, and also may require the object to carry fluid to be injected.